How to get file upload progress in Node.js?

var fs = require('fs');
var express = require('express');
var multer = require('multer');
var progressStream = require('progress-stream');
var app = express();
var upload = multer({ dest: 'upload/' });
app.post('/upload', function (req, res, next) {
  // 创建progress stream的实例
  var progress = progressStream({length: '0'}); // 注意这里 length 设置为 '0'
  req.pipe(progress);
  progress.headers = req.headers;
  // 获取上传文件的真实长度（针对 multipart)
  progress.on('length', function nowIKnowMyLength (actualLength) {
    console.log('actualLength: %s', actualLength);
    progress.setLength(actualLength);
  });
  // 获取上传进度
  progress.on('progress', function (obj) {    
    console.log('progress: %s', obj.percentage);
  });
  // 实际上传文件
  upload.single('logo')(progress, res, next);
});
app.post('/upload', function (req, res, next) {
  res.send({ret_code: '0'});
});
app.get('/form', function(req, res, next){
  var form = fs.readFileSync('./form.html', {encoding: 'utf8'});
  res.send(form);
});
app.listen(3000);

// 获取上传文件的真实长度（针对 multipart)
progress.on('length', function nowIKnowMyLength (actualLength) {
  console.log('actualLength: %s', actualLength);
  progress.setLength(actualLength);
});

tr.on('pipe', function(stream) {
  if (typeof length === 'number') return;
  // Support http module
  if (stream.readable && !stream.writable && stream.headers) {
    return onlength(parseInt(stream.headers['content-length'] || 0));
  }
  // Support streams with a length property
  if (typeof stream.length === 'number') {
    return onlength(stream.length);
  }
  // Support request module
  stream.on('response', function(res) {
    if (!res || !res.headers) return;
    if (res.headers['content-encoding'] === 'gzip') return;
    if (res.headers['content-length']) {
      return onlength(parseInt(res.headers['content-length']));
    }
  });
});